1. Field of the Invention
The present invention relates to a composition which is used to for limiting and attenuating the visible symptoms of natural or accidental ageing of the skin. It applies both to natural ageing (anti-ageing action) and to phenomena of accidental ageing of the skin due to the many attacking factors to which the skin is subjected daily, in particular those caused by solar radiation (antisun products and after-sun products).
In general, it is known that ageing is an unavoidable phenomenon, but certain factors can accelerate the process. It is known that the ultraviolet radiation of light adversely affects the normal functions of the skin and that prolonged exposure to solar radiation contributes towards ageing and to the induction of skin cancers. Free radicals are the main agents incriminated in these adverse changes.
Free radicals are corrosive particles which have a free electron, of great chemical reactivity, and are thus particularly unstable.
They are generated by ionizing radiation, ultraviolet radiation and even visible sunlight, but they are also derived from the metabolic and enzymatic reactions which take place in the body. These reactions take place, for example, during cell respiration, in the mitochondria, or during the synthesis of prostaglandins, in the course of the inflammation process, or alternatively during phagocytosis.
A free radical can form according to two types of chemical process:
homolytic cleavage of a single chemical bond between two atoms in a molecule, each taking one electron from the bond with it: ##EQU1## transfer of an electron (redox reaction) between two molecules (an oxidizing agent and a reducing agent) which gives rise to two charged radicals: ##EQU2## PA1 poor food hygiene PA1 prolonged and repeated exposure of the body to ionizing radiation (X-rays, UV rays, excessive sunbathing) PA1 poor use of medicaments and abuse of tobacco or alcohol PA1 pollution PA1 stress, which is an indirect promoter of free radicals, etc. PA1 reactions resulting in the production of the hydroxyl radical OH., PA1 those derived from haems, such as free haemoglobin, which produces oxoferryl-type radicals. PA1 has very good anti-radical properties, so as to obtain an anti-ageing action for both natural and accidental ageing, PA1 affords effective protection against the reactions which result in the production of OH. radicals or oxoferryl-type radicals, PA1 reduces the fall in the ATP content of keratinocytes after irradiation, so as to obtain a repairing effect. PA1 hepatitis, PA1 colopathies, PA1 ictero-haemorrhagic syndromes, PA1 urinary and bile lithiases, PA1 cardiovascular and circulatory pathologies, etc. PA1 A dark brown coloration which leads to intense mustard-yellow staining of the skin to be treated, as well as of the fingers used to apply the product. The high intensity of this staining is attenuated by rinsing, but a dark yellow coloration remains after washing. PA1 Poor stability over time: from 24 hours onwards, concentration of water in the bottom of the container and considerable release of oil at the surface are observed. PA1 A strong odour of plant extract. PA1 Excessively intense colour not at all in keeping with what consumers using cosmetic products will generally find acceptable. PA1 Product acting essentially as a dye: the skin and the nails are unavoidably stained a more or less pronounced yellow. Similarly, tissues which come into contact with this product are indelibly stained a more or less pronounced yellow which turns to orange after washing with the usual detergents.
The most common reaction resulting from having free radicals in solution is the stripping of a hydrogen atom from a substrate present in the medium, which leads to the formation of a new free radical: ##EQU3##
The radical-mediated attack initiates chain reactions which stop only when two free radicals mutually inactivate themselves.
Lipid peroxidation (lipoperoxidation) is a typical case of a radically-induced chain reaction.
The oxidation of membrane lipids results in the formation of lipoperoxides, which decompose into various fragmentation products, some of which are highly corrosive.
One of the most important and most corrosive fragmentation products is an aldehyde, malondialdehyde (MDA). Since this molecule bears two free radicals, it exhibits formidable toxicity by bridging across proteins, intracellular lipids and DNA.
In the toxicity of free radicals towards biological systems, oxygen-derived reactive species occupy a predominant position.
The main radical species involved in biological processes are the following:
______________________________________ .sup.1 O.sub.2 singlet oxygen O.sub.2.sup..cndot.- superoxide anion radical which induces the formation of a much more reactive radical: OH.sup..cndot. hydroxyl radical, very powerful oxidizing agent HOO.sup..cndot. perhydroxyl radical (protonated form of O.sub.2.sup..cndot.-) LO.sup..cndot. lipid alkoxyl radical LOO.sup..cndot. lipid peroxyl radical ______________________________________ (L = polyunsaturated phospholipid group)
The free radicals and the cascade of chain reactions which they generate in the body play a very important role in the process of ageing of the skin.
Their destructive action on membrane lipids results in the slow death of cells.
They also attack the genetic patrimony of cells: DNA and RNA, which are essential molecules for protein synthesis reactions.
Lastly, they degrade proteins, in particular collagen fibres and elastic fibres, the functional characteristics of which are severely impaired.
The results of all this are damaged, prematurely aged skin.
Now, cell metabolism (in particular respiration) generates free radicals. This is an entirely normal phenomenon which cells are capable of combating since they are equipped with suitable means of defence.
In certain circumstances, this harmonious equilibrium can be broken. The natural protection system of the cell is then no longer sufficiently effective. Many causes trigger a breakdown in the equilibrium of cells with respect to free radicals:
Various means exist in cells for opposing and neutralizing free radicals: protective agents, enzymes (superoxide dismutase, glutathione peroxidase and catalase), certain trace elements (zinc, selenium) and vitamins (vitamins A-C and especially E).
However, a certain number of radicals escape this natural defence. This can, in the long run, lead to a cumulative phenomenon which arises in the process of senile involution and wear.
2. Description of the Prior Art
In order to combat this phenomenon, anti-radical compounds have already been proposed which help the natural defence systems of cells in order to allow the body to recover harmonious functioning. These compounds, just like the molecules naturally present in the skin, form with free radicals, on account of chemical, physicochemical and electrochemical affinities that are much greater for free radicals than for the membrane structures, stable, non-radical products.
Depending on their nature, the anti-radical substances block the chain reaction at various stages, thus more or less rapidly stopping the radical-mediated attack. In this way, the lipid membranes are preserved.
It is also recalled that, in living beings, cells are affected by various types of oxidative reaction, including the following two reactions:
Moreover, it is known that the content of ATP (adenosine triphosphate, the main energetic substrate of cells) in human epidermal keratinocytes partly reflects the energetic state of cells: ATP, the molecule for transferring and storing energy, is essential for cell metabolism.
It has been observed during experiments that the content of ATP in keratinocytes falls significantly after exposure to radiation such as, for example, ultraviolet radiation (UVB).